Abstract:

There is provided a system and a method for quantitative measurement of
spasticity in a patient. It has been found that stretch reflex
measurements, that are quantitatively indicative of spasticity, can be
obtained by recording an EMG signal while the limb is being moved at a
variety of angular velocities. The method advantageously allows the
clinician to perform the test at the bedside by eliminating the need for
cumbersome mechanical components for moving the limb while providing
quantitative measurements.

Claims:

1. A method for providing a quantitative measure of spasticity in a limb,
comprising:a) providing measurement apparatus for measuring a joint angle
and EMG activity in said limb;b) determining a threshold EMG activity
value in said limb;c) determining a zero angle defining an initial
position of said limb;d) imparting a movement to said limb from said
initial to a final position while measuring an EMG activity value in
muscles of said limb and angles and velocities at which said limb is
moved;e) recording angle and velocity as a data point at which said
measured EMG value crosses said threshold EMG activity value;f) repeating
said movement at a range of velocities until a set of data points are
acquired and recorded; andg) processing said set of data points and
computing a threshold angle value and a sensitivity of said threshold
angle to velocity value, said values providing a quantitative measure of
spasticity in said limb.

2. The method as claimed in claim 1 wherein said movement is imparted to
the limb by a clinician.

3. The method as claimed in claim 2 further comprising providing feedback
to said clinician during data acquisition to allow said clinician to
choose appropriate values for said range of velocities.

4. The method as claimed in claim 3, further comprising controlling said
acquisition of said data points for recording a set of converging data
points and minimizing processing errors by determining a velocity for
moving said limb and providing an indication of said velocity to said
clinician.

5. The method as claimed in claim 4 wherein said providing an indication
of said velocity comprises providing a sweep audio sound or a visual
signal describing said velocity for moving said limb and wherein said
moving is performed in accordance with said sweep audio sound or said
visual signal.

6. The method as claimed in claim 1 further comprising displaying said set
of data points by plotting said angle and said velocity values.

7. The method as claimed in claim 6 wherein said displaying comprises
displaying a best fit graph of said data points.

8. The method as claimed in claim 7 further comprising validating said set
of data points by viewing said best fit graph of said set of data points
and removing any outlying data points.

9. The method as claimed in of claim 1 further comprising determining an
upper angle value and a lower angle value determining a biomechanical
range of the limb joint angle and wherein said quantitative measure of
spasticity is expressed as a spasticity level from one of said threshold
angle value, said upper angle value and said lower angle value.

10. The method as claimed in claim 1, wherein said measuring of said
angles and said velocities comprises attaching a goniometer to said limb
for measuring a joint angle value and an angular velocity value and
determining an angle voltage value and a velocity voltage value.

11. The method as claimed in claim 1, further comprising validating a
regularity of said motion of said limb and wherein said angle and
velocity values are recorded as a data point if said motion is valid.

12. A system for providing a quantitative measure of spasticity in a limb,
said system comprising:a) a joint angle sensor capable of detecting
angular motion in said limb;b) an angular velocity determinator;c) an EMG
detector for measuring stretch reflex activity in said limb;d) an EMG
signal threshold determinator for determining onset of stretch reflex
activity;e) a zero set to record a zero angle;f) a stretch reflex
detector for recording velocity and angle data at onset of stretch reflex
activity;g) spasticity evaluator module to process said angle and
velocity data recorded at onset of stretch reflex activity and provide a
measure of spasticity;h) acquisition control/user feedback allowing a
clinician to activate settings and for guiding said clinician in a choice
of a range of velocities for data acquisition, andi) a data quality
evaluator for evaluating a quality of said measure of spasticity provided
by said spasticity evaluator module and generating a signal to said
acquisition control/user feedback that is reflective of said quality.

13. The system as claimed in claim 12 wherein said joint angle sensor is
selected from a goniometer and a motion capture system.

14. The system as claimed in claim 13 wherein said goniometer is selected
from potentiometer, optical encoder, or bend sensor.

15. The system as claimed in claim 12 further comprising a motion
validator to validate and accept/reject clinician generated limb motion
data.

16. The system as claimed in claim 12 wherein said acquisition
control/user feedback means comprises a user controlled foot pedal for
activating settings.

17. The system as claimed in claim 12 wherein said spasticity evaluator
module provides said acquisition control/user feedback means with desired
velocities of acquisition.

18. The system as claimed in claim 17 wherein said acquisition
control/user feedback means provide feedback signal to prompt said
clinician to acquire additional measurements at said desired velocities.

19. The system as claimed in claim 18 wherein said feedback signal is
selected from an audio sweep signal and a visual signal indicative of
said desired velocity to be imparted to a limb during flexing/stretching
measurements.

20. The system as claimed in claim 12 further comprising data storage
means.

21. The system as claimed in claim 12 further comprising a display for
displaying results and/or instructions to said clinician.

22. The system as claimed in claim 12 further comprising a quiet detection
module for determining a starting position of said limb.

23. The system as claimed in claim 12 further comprising a motorized limb
motion effector for automatically imparting motion to a limb.

24. A method of patient care to reduce spasticity and/or to improve motor
control of a limb, the method comprising:administering physical,
pharmacological or surgical treatment to the patient;a) providing
measurement apparatus for measuring a joint angle and EMG activity in
said limb;b) determining a threshold EMG activity value in said limb;c)
determining a zero angle defining an initial position of said limb;d)
imparting a movement to said limb from said initial to a final position
while measuring an EMG activity value in muscles of said limb and angles
and velocities at which said limb is moved;e) recording angle and
velocity as a data point at which said measured EMG value crosses said
threshold EMG activity value;f) repeating said movement at a range of
velocities until a set of data points are acquired and recorded; andg)
processing said set of data points and computing a threshold angle value
and a sensitivity of said threshold angle to velocity value, said values
providing a quantitative measure of spasticity in said limb; andassessing
an efficacy of said administering using said quantitative measure.

25. A use of the system as claimed in claim 12 for measuring spasticity in
a limb.

Description:

FIELD OF THE INVENTION

[0001]This invention relates to the field of muscle activity assessment
and more specifically to the assessment of spasticity in muscles.

BACKGROUND OF THE INVENTION

[0002]Spasticity is a neurological symptom affecting children and adults
causing an abnormal increase in muscle tone that occurs when the affected
muscle is stretched. Spasticity can occur in neurological disorders that
damage the parts of the brain and the nervous system that control
voluntary movements. The most common disorders leading to spasticity are
cerebral palsy, spinal cord injury, multiple sclerosis, stroke, and
traumatic brain injuries, due to a lack of oxygen, physical trauma,
haemorrhage, or infection. Some of these injuries can occur at birth and
others can occur during adulthood.

[0003]The severity of spasticity can range from slight muscle stiffness to
deformity and permanent muscle shortening, called contracture. Spasticity
often interferes with voluntary movement and with the proper positioning
of the body. The presence of spasticity interferes with the
accomplishment of activities of daily living such as dressing, eating,
and grooming. Spasticity also interferes with mobility, seating and
transfers such as moving from the bed to the wheelchair or from sitting
to standing. Spasticity also may make it difficult to sit comfortably, or
to change positions frequently enough to prevent joint pain and pressure
sores. Spasticity in the feet can prevent comfortable fitting of shoes.
Severe spasticity may cause painful joint misalignments and limitations
in joint movement interfering with hygiene.

[0004]Physical, pharmacological and surgical therapies are aimed at
decreasing spasticity and restoring motor control. Physical treatments
include stretching and positioning to prevent the development of muscle
contractures. Pharmacological approaches include oral or intrathecal
delivery of drugs targeting the neuromuscular junction of the muscle or
the synaptic pathways and nerves innervating the muscle. Local injections
of drugs that weaken or paralyze overactive muscle (chemodenervation
agents) can be effective for spasticity in isolated muscles. Severe
spasticity that cannot be effectively treated with drugs or injections
may respond to surgical destruction of some overactive nerves in the
spine. Contracture may be treated with serial casting to allow tendons to
stretch, or orthopedic surgery if required.

[0005]A major problem in the treatment of spasticity is that a sensitive
measure of the phenomenon that can be applied at the bedside or in the
clinic to make treatment decisions and to judge the effectiveness of
treatment does not yet exist. Until now, a variety of different clinical
measures have been used to assess spasticity. The current `gold standard`
is a 5 point scale (Ashworth Scale) that can only distinguish the
presence or absence of spasticity but is not sensitive to its severity.
What is more, the scale is subjective, so that the evaluator must `judge`
how much resistance is felt when he or she stretches the muscle.
Clinicians and researchers agree that this measure is inadequate since it
does not discriminate between different types of hypertonicity and does
not adequately reflect the severity of spasticity. Furthermore while
apparatuses exist for obtaining spasticity measurements that use
mechanical components to apply a torque to a joint, they are cumbersome
and difficult to adapt to the various types of joints and may create
discomfort in the patient.

[0006]The identification of the need to have a better (more sensitive and
discriminative) measure of spasticity that is easily accessible to the
clinician has been apparent for many years.

SUMMARY OF THE INVENTION

[0007]There is provided a system and a method for quantitative measurement
of spasticity in a patient. It has been found that stretch reflex
measurements, that are quantitatively indicative of spasticity, can be
obtained by recording an EMG signal while the limb is being moved at a
variety of angular velocities. Each movement of the limb from an initial
to a final position need not be performed at constant velocity and
therefore the method advantageously allows the clinician to perform the
test at the bedside by eliminating the need for cumbersome mechanical
components for moving the limb while providing quantitative measurements.

[0008]Thus, there in one aspect of the invention there is provided a
method for providing a quantitative measure of spasticity in a limb,
comprising providing measurement apparatus for measuring a joint angle
and EMG activity in the limb, determining a threshold EMG activity value
in the limb, determining a zero angle defining an initial position of the
limb, imparting a movement to the limb from the initial to a final
position while measuring an EMG activity value in muscles of the limb and
angles and velocities at which the limb is moved, recording angle and
velocity as a data point at which the measured EMG value crosses the
threshold EMG activity value, repeating the movement at a range of
velocities until a set of data points are acquired and recorded, and
processing the set of data points and computing a threshold angle value
and a sensitivity of the threshold angle to velocity value, the values
providing a quantitative measure of spasticity in the limb.

[0009]In another aspect there is also provided a system for providing a
quantitative measure of spasticity in a limb, the system comprising, a
joint angle sensor capable of detecting angular motion in the limb, an
angular velocity determinator, an EMG detector for measuring stretch
reflex activity in the limb, an EMG signal threshold determinator for
determining onset of stretch reflex activity, a zero set to record a zero
angle, a stretch reflex detector for recording velocity and angle data at
onset of stretch reflex activity, spasticity evaluator module to process
the angle and velocity data recorded at onset of stretch reflex activity
and provide a measure of spasticity, acquisition control/user feedback
allowing a clinician to activate settings and for guiding the clinician
in a choice of a range of velocities for data acquisition; and a data
quality evaluator for evaluating a quality of the measure of spasticity
provided by the spasticity evaluator module and generating a signal to
the acquisition control/user feedback that is reflective of the quality.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010]FIG. 1 is a schematic representation of an embodiment of the
apparatus of the invention for determination of spasticity;

[0011]FIG. 2 is flow chart of an embodiment of the method for
determination of spasticity;

[0012]FIGS. 3 A and B are graphs showing results of stretch reflex
thresholds determined in one patient at two different times; and

[0013]FIG. 4 is a diagram of an embodiment of the system of the present
invention.

DETAILED DESCRIPTION OF THE INVENTION

[0014]There is provided a method and apparatus that advantageously
measures spasticity in an objective and reproducible way. Referring to
FIG. 1 a schematic diagram of spasticity measurements being performed on
a limb according to an embodiment of the method of the present invention
is shown. The set up allows the acquisition of EMG signals, joint angles
Θ and angular velocities ω data that are used to provide a
quantitative measurement of spasticity. In FIG. 1 an arm 10 is shown in
which the elbow (the joint) is bent at an angle Θ. A joint angle
sensing device such as a goniometer 12 is attached to the arm to provide
angle measurements and muscle activity is monitored by an EMG 14
comprising electrodes 15. The data is processed by data processor 16 to
assess spasticity by computing the angle λ at which the onset of
the stretch reflex (SR) is triggered. The results may be compared to
results obtained for normal individuals or individuals with similar or
different diseases.

[0015]In one embodiment, and referring to FIG. 2, the method of the
present invention comprises providing at 20 means for sensing angles of a
moving joint. At 22 a threshold EMG activity value is determined in the
limb that corresponds to the onset of the SR activity. This threshold can
be determined by the clinician in a measurement session by acquiring a
plurality of EMG while the joint is being flexed/stretched. The threshold
generally corresponds to the angle at which an EMG signal value rises
above a value considered to be statistically different from the baseline.
Next an angle (zero angle) at which no EMG activity is detected (rest
position) is determined at 24. Measurement angles Θ are defined
relative to the zero angle. It will be appreciated that the zero angle
may vary from patient to patient and that it may correspond to either the
"open" or "closed" position of the joint. Assessment of spasticity is
based on the static stretch reflex threshold (SRT) which is the joint
angle at which the muscle start to be activated. While this angle can be
determined using a "static" approach (by quasi-statically stretching the
muscles), it is preferred to determine the SRT using a dynamic approach
in which the limb is moved and the angular velocity of the joint is
recorded as a function of the angle. For each velocity of stretch, the
angle at which the onset of SR is detected is recorded and a regression
is performed to obtain the static SRT angle at velocity zero. Thus,
referring back to FIG. 2, the clinician performs, at 26 and 30, a series
of flexions/extensions of the joint at a plurality of velocities while
the EMG activity, the angle and the angular velocity are measured. For
each flexion/extension, the angle and the velocity at which the EMG
threshold is crossed are recorded at 28 and the data are processed at 32
to determine SRT and assess spasticity. It will also be appreciated that
an upper and a lower angular limit may be determined which may serve as a
basis, together with the SRT angle, to assess spasticity.

[0016]It was found that the velocity at which the limb is moved from an
initial to a final position need not be constant thereby allowing a
clinician to impart the motion to the limb and eliminating the need for a
controlled motorized motion of the limb. However, it will be appreciated
that a simple motorized limb flexor that does not necessarily comprise
elaborated velocity controlling elements, which would therefore be better
suited for easy and convenient bedside measurements, may also be used.

[0017]During the procedure, feedback is preferably provided to the
clinician by, for example, displaying the EMG traces, the angles, the
angular velocity and SRT results. Such feedback allows the clinician to
properly adjust the baseline EMG threshold and the zero angle prior to
beginning the measurement and to assess the quality of data acquisition
during or after measurement. Feedback can also be provided to the
clinician to prompt him or her to acquire additional measurements at
angular velocities different from those already recorded to minimize the
error on the determination of SRT.

[0018]The SRT can be determined by interpolating the data using the SR
threshold at each velocity so as to obtain the SR angle at zero velocity.
The data can be fitted using a regression analysis as would be known to
those skilled in the art. The equation characterizing the line is:

+μω-λ=0

[0019]wherein ω=dΘ/dt, and μ is the sensitivity of the
threshold λ to velocity. The sensitivity μ and threshold λ
are used to characterize the level of spasticity. The results
surprisingly showed that the method is robust with regard to variations
in the velocity at which the limb is moved. That is to say, the velocity
need not be constant during a flexion/extension acquisition therefore
making it possible for a clinician to move the limb as opposed to using a
mechanically controlled apparatus to apply a torque to the limb. This
advantageously allows the measurements to be performed at bedside in a
minimum amount of time.

[0020]Referring to FIG. 3, an example of angle-velocity curves measured
with an embodiment of the device of the present invention is shown. The
graphs show results of two measurement sessions performed on the same
patient by the same therapist at two different times. The patient is a 69
year old male patient who had a stroke resulting in left-sided paresis, 2
years ago. The computed stretch reflex thresholds were 127 deg and 139
deg in this test-retest.

[0021]In another aspect of the invention, there is provided a system for
obtaining spasticity measurements which comprises a joint angle sensor
capable of detecting angular motion in said limb, an angular velocity
determinator, an EMG detector for measuring stretch reflex activity in
the limb, an EMG signal threshold determinator for determining onset of
stretch reflex activity, a zero set to record a zero angle, a stretch
reflex detector for recording velocity and angle data at onset of stretch
reflex activity, spasticity evaluator module to process said angle and
velocity data recorded at onset of stretch reflex activity and provide a
measure of spasticity, a data quality evaluator; and an acquisition
control/user feedback module allowing a clinician to activate settings
and for guiding the clinician in a choice of a range of velocities for
data acquisition. Spasticity can also be expressed as a function of
λ and the biomechanical range of the joint angle.

[0022]An embodiment of the system is shown in FIG. 4. The system comprises
a joint angle sensor 40 which allows the detection of the joint angle as
a function of time from which the velocity can be derived. The sensed
angle and the derived velocity are converted to electrical signals by
angle to voltage 42 and velocity to voltage 44 circuits which provide
input data to the stretch reflex detector 46. The angle also serve as
input data to the threshold determinator 48 which also receives input
data from EMG measurement unit 50. The threshold determinator 48
establishes the threshold that defines the onset of stretch reflex
activity that is subsequently used to detect a spasticity event. The
angle data is also fed into the zero set unit 52 that records the
clinician determined zero angle defined above. Stretch reflex detector
outputs the velocity and the angle detected at or just before detection
of the stretch reflex signal which occurs when the threshold is crossed.
The velocity and angle data at the onset of the stretch reflex event are
fed into spasticity evaluator module 54 which also receives the position
for the zero angle as input data. Spasticity evaluator 54 can then
perform the necessary data processing for determining λ and μ
(angle of SRT and sensitivity) that are indicative of the degree of
spasticity. The results can be displayed on display 56. It will be
appreciated that display 56 can also display EMG traces, angle
measurements, velocity data and the like to provide feedback to the
clinician.

[0023]A quiet detection module 58 is provided that processes data from the
zero set 52, EMG measurement unit 50 and angle to voltage circuit 44 to
determine when the limb is in an appropriate starting position. For
example, the starting position could be defined by the angle Θ
being within ±10 degrees of the zero angle and by the EMG being quiet
for a certain amount of time, for example 5 seconds. It will be
appreciated that other starting conditions could be defined depending on
the joint, disease and other factors as would be obvious to one skilled
in the art. The quiet detection module generates a quiet signal that is
forwarded to the acquisition control/user feedback module 60 which in
turn can generate a signal, such as an audio signal, to alert the
clinician that measurements can be started. Acquisition control/user
feedback module 60 may also generate other signals to guide the clinician
in the acquisition of data. For example, the clinician could be prompted
to acquire additional data for the spasticity evaluator module 54 to
improve spasticity assessment. Thus a data quality evaluator can be
provided that can analyze, for example by performing a statistical
analysis, the measured spasticity value and send a signal to the
acquisition control/user feedback module that will encode necessary
information to prompt the user to acquire additional signal. The user
may, based on the signal, adjust the speed at which the limb is moved,
modify the zero angle and the like. The actual velocity may be recorded
whether or not it corresponds to the requested velocity. For example a
glissando (sweep) audio signal can be generated to indicate at which
velocity the limb should be moved. Alternatively a visual signal such as
an animation showing the movement so that the clinician can adjust the
speed to match that of the animation. The animation can be repeated at
intervals to allow the clinician to adjust by repeating the motion
several times. The acquisition control/user feedback module may comprise
a foot pedal enabling the user/clinician to activate settings, such as
recording the threshold and the zero angle, using his/her foot thereby
freeing his/her hands to manipulate the limb.

[0024]Additional options and features of the system are now described.
They are intended to be exemplary and do not limit the scope of the
invention.

[0025]Optionally the system may comprise a motion validator 30 to validate
angle and velocity measurements and accept/reject data based on
predetermined criteria or ranges for these data. For example it may be
desirable to move the limb within a range of velocities. Thus the motion
validator can reject measurements if the variation in the velocity
imparted to the limb falls outside a predetermined range.

[0026]The system can operate in real time to provide instant feedback to
the clinician. However it will be appreciated that the system can be
computerized to allow storage and later retrieval/processing of the data.

[0027]The joint angle can be measured by a goniometer or by a motion
capture system, for example. The goniometer sensing could be by
potentiometer, optical encoder, or bend sensor. Furthermore, the output
of the joint angle sensor could be a voltage, a series of pulses from an
incremental optical encoder, or a parallel output from an absolute
optical encoder. The angle information can be sent to the computer input
via a wire or via a radio signal such as Bluetooth or ZigBee.

[0028]The angular velocity can be obtained by analog differentiation of
the voltage signal from a potentiometric goniometer. If the goniometer
uses an incremental optical encoder the velocity can be measured as the
reciprocal of the time between successive pulses. Similarly, if an
absolute encoder is used, the velocity could be measured as the
reciprocal of the time between changes in absolute output.

[0029]When measuring individuals with spasticity, false readings may be
obtained due to limb positioning or the voluntary movements made by the
individual. Some of these signals can be determined to be incorrect
algorithmically by the motion validator 62, and hence ignored by the
program. The examiner can also remove incorrect data points immediately
after they occur by pressing a foot switch, or later when the data set is
presented. Some of these false data points will be displayed as outliers
that can also be removed algorithmically.

[0030]As mentioned above, the data required by the spasticity evaluator
module are the velocity and angle. Preferably these data are those
acquired 30 ms before the EMG event. Therefore, a memory of the movement
extending back at least 30 ms should preferably be maintained. In fact,
the complete acquisition from start to end is preferably retained. That
is, the velocity, angle, and complete EMG waveform are available to the
clinician and can be viewed in various ways as overlaid graphs, for
example.

[0031]The threshold is set by adjusting the amplitude of the EMG signal so
that the response of the spastic muscle is greater than a fixed reference
value. This level setting can be done by a potentiometer or by a variable
gain amplifier. The gain of the amplifier could be set algorithmically
during the set-up. The foot switch may be used to indicate to the program
that the EMG threshold should be set during the subsequent movements.

[0032]The threshold level is a fixed level. When the EMG signal exceeds
the reference level, the threshold signal is generated. The reference can
be exceeded on either the positive or negative excursion of the EMG
signal. This can be detected digitally by ignoring the most significant
bit (msb) of the digitized EMG signal. (If the EMG is assumed to be
converted to a signed integer, the sign is determined by the msb) If the
threshold is measured in an analog circuit before acquisition, the EMG
signal can be full-wave-rectified before going to the threshold
determinator.

[0033]The EMG signal is generated by placing electrodes on the patient.
The electrodes are placed on a specific muscle so that consistent
measurements are made between and among patients. Holding and moving the
limb should also be done consistently for all patients. An EMG Measuring
Unit is typically an instrumentation amplifier with low-pass and
high-pass filtering. The low-pass filter removes frequencies above one
half of the sampling frequency of the data acquisition device to avoid
aliased signals. The high-pass filter removes motion artifacts, which are
electrical signals generated by movement of the electrodes on the skin or
by movement of the wires (if present).

[0034]A predetermined minimum number of data points should be collected to
generate a meaningful result. After collecting the minimal data set, the
program performs a linear regression as each new data point is collected.
When the confidence interval is below some predetermined size, the
program reports that it has found the spastic deficit. The program could
also examine the data set to ignore outliers.

[0035]The display can be a 1/4 VGA screen, such as an LCD type. The
display can be used to display instruction manual, tutorials, correct
placement of electrodes and goniometer, movies showing an examiner
performing the movements, and display of results.

[0036]The device is designed to measure the severity of spasticity. It can
potentially be used to measure spasticity at the wrist, elbow, shoulder,
ankle, knee and hip. It can be used in the research laboratory, at a
patient's bedside in the hospital ward, in a medical clinic, in a
rehabilitation center or in a patient's home. Patients in whom the
measurement of spasticity is needed include but is not limited to
children and adults with cerebral palsy or other congenital diseases,
adults with stroke, brain injury, multiple sclerosis, amylotrophic
lateral sclerosis, spinal cord injury, and other neuromuscular disorders.
Measurement of the stretch reflex threshold can be used to quantify
spasticity and to monitor patient progress following the administration
of physical, pharmacological or surgical treatments to reduce spasticity
and to improve motor control.

[0037]The device may be used by physiotherapists, occupational therapists,
nurse practitioners, medical doctors (neurologists, orthpaedists,
surgeons) and researchers. It will be appreciated that such persons
skilled in the art would be capable of operating the device of the
invention including selecting appropriate muscles for placing electrodes
for EMG recordal.

[0038]While the invention has been described in connection with specific
embodiments thereof, it will be understood that it is capable of further
modifications and this application is intended to cover any variations,
uses, or adaptations of the invention following, in general, the
principles of the invention and including such departures from the
present disclosures as come within known or customary practice within the
art to which the invention pertains and as may be applied to the
essential features herein before set forth, and as follows in the scope
of the appended claims.